Energy Dissipation of Hydraulic Support Columns under Rockfall Impact Load in Steeply Dipping Coal Seams
Round 1
Reviewer 1 Report
1. The mechanical models in this paper are not clear.
2. Numerical models are not clear and lack necessary process of the simulations.
3. The values of parameters used in the simulation are unreasonable.
4. Some technical terms used in this paper are inaccurate, for instance, support column, roof leakage, floor slip, et al.
5. Lots of grammar and spelling errors in the paper.
6. Suggest adding some articles in the international journals as the references.
Lots of grammar and spelling errors in the paper, such as capital letters, blank space between the value and units, punctuation, and similar errors.
Author Response
Response to Reviewer 1Comments
Point 1:The mechanical models in this paper are not clear.
Response 1:Thanks for the comment, the mechanical model of this paper mainly involves the rockfall migration model and the rockfall impact hydraulic support column model. The rockfall migration model is mainly simulated by PFC3D software, which has supplemented its basic theory and iterative process. See line 117 - 145. And the numerical simulation model of rockfall and working face is supplemented as shown in Fig.5. In this paper, the hydraulic support column model is derived from the ZZ6500/22/48 hydraulic shield support on the working face site. This modification supplements the engineering drawing and numerical simulation diagram of the support, as shown in Fig. 7, and also supplements the relevant parameter information of the support, see line 294-300.
Point 2:Numerical models are not clear and lack necessary process of the simulations.
Response 2:In this paper, the rockfall migration model is simulated by the particle flow PFC program. The basic theory has been discussed in line 117-145 in the text, and the iterative process diagram is also supplemented in the text, as shown in Fig. 3.As for the simulation of the collision process between rockfall and column, it is obtained by programming simulation according to the formula in this paper, and the process can be referred to the order of the formula in this paper.
Point 3:The values of parameters used in the simulation are unreasonable.
Response 3:The values of parameters used in the simulation are taken from references. The parameters of this paper were selected by referring to the geological conditions of the 25221 working face of the Aiweiergou 2130 coal mine in Urumqi, Xinjiang, China. The property parameters of the regular hexahedral rockfall and the working face are shown in Tables 1 and 2 [23], [27]. The column parameters are derived from the ZZ6500 / 22 / 48 hydraulic shield support [43].
Point 4:Some technical terms used in this paper are inaccurate, for instance, support column, roof leakage, floor slip, et al.
Response 4:This article has been modified, such as “support column” has been modified to “hydraulic support column”, “roof leakage” has been modified to “roof fall”. After the modification of this article, there is no content involving “floor slip”, which has been deleted.
Point 5: Lots of grammar and spelling errors in the paper.
Response 5:This article has been polished by the MDPI official website, and there are no grammar and spelling errors.
Point 6: Suggest adding some articles in the international journals as the references.
Response 6:We have added 12 references and revised the introduction. See lines 32-49.
Point 7: Comments on the Quality of English Language. Lots of grammar and spelling errors in the paper, such as capital letters, blank space between the value and units, punctuation, and similar errors.
Response 7:This revised draft has been polished by the MDPI official website, and there are no grammar and spelling errors.
Reviewer 2 Report
The paper uses theoretical analysis and numerical simulation to construct the contact model of the shock process between polyhedron rockfall and the hydraulic support column, and compares the effects the influence of rockfall velocity, side length, elastic modulus and density on the maxi-mum deformation, maximum impact force and energy absorption of the column is analyzed. The study is complete and interesting, but the current version of this manuscript can not meet the standard of publication and it requires some work before the consideration of publication. After careful consideration, I recommend that this paper can be published after a major revision.
Possible suggestions are as follows:
(1) The content of the abstract is not concise enough, please further optimize the content of the abstract to express the content of the article.
(2) The article notes “The energy tracking method ( ETM ) is compared with the trajectory which is established by PFC”, Please provide additional information and elaborate on the numerical simulation models and the computational processes involved.
(3) The paper utilizes numerical simulation to investigate the collision process between rockfall and column. However, it does not present the corresponding numerical models and simulation results. Please provide supplementary information to ensure the validity and reliability of the extracted data.
(4) The paper mentions that rockfall cause deformation in hydraulic columns and analyzes the relationship between energy loss and maximum contact deformation during the collision process between rockfall and hydraulic supports. The obtained patterns are essentially consistent, and the content reflected by both approaches is repetitive. It is suggested to simplify and streamline the presentation accordingly.
(5) The article states that " according to the Hertz contact theory, the contact model of the shock process between polyhedron rockfall and the hydraulic support column is constructed, and the maximum deformation and maximum impact force of the collision contact between the rockfall and the column are obtained. Finally, the Hamilton principle and the Galerkin discrete method are used to construct the dynamic model of the collision between the rockfall and the column, and the energy evolution law of the shock process between rockfall and the column is studied" However, the paper does not present the parameters used in the calculations nor the computed results. Additionally, it fails to highlight the application of this model in numerical simulations. Furthermore, there is no comparison made between the numerical simulation results and the calculation results obtained from theoretical analysis, which is essential to validate the reliability of the findings.
(6) References section: It is striking that all papers referenced are from Chinese authors; the literature review produced as a whole is very China-focused/restricted.
(7) The paper investigates the "Energy dissipation of support column structure under rockfall impact load in steeply dipping coal seams." However, it does not provide information regarding the deformation of hydraulic columns in the field or the parameters of the rockfall. It is unclear whether the results obtained from numerical simulations can be directly applied to real-world scenarios. I suggest the authors to further supplement the paper with relevant field data to support their findings.
Author Response
Response to Reviewer 2Comments
Point 1: The content of the abstract is not concise enough, please further optimize the content of the abstract to express the content of the article.
Response 1:The abstract has been extensively revised and polished by the MDPI official website.
Point 2:The article notes “The energy tracking method ( ETM ) is compared with the trajectory which is established by PFC”, Please provide additional information and elaborate on the numerical simulation models and the computational processes involved.
Response 2:The rockfall migration model is mainly simulated by PFC3D software, which has supplemented its basic theory and iterative process. See line 122 - 145, and the iterative process diagram is also supplemented in the text, as shown in Fig. 3. The ETM method is widely used to simulate rockfall migration on the ground slope and rockfall migration in underground SDCSs [28]-[31], [38]-[42]. It has been explained in lines 276-277.
Point 3:The paper utilizes numerical simulation to investigate the collision process between rockfall and column. However, it does not present the corresponding numerical models and simulation results. Please provide supplementary information to ensure the validity and reliability of the extracted data.
Response 3:The numerical model in this paper is that the middle position of the fixed beam at both ends is impacted by rockfall. It is mentioned in lines 148-150 and 191-192.The simulation results are discussed in detail in Figs.8-11.
Point 4:The paper mentions that rockfall cause deformation in hydraulic columns and analyzes the relationship between energy loss and maximum contact deformation during the collision process between rockfall and hydraulic supports. The obtained patterns are essentially consistent, and the content reflected by both approaches is repetitive. It is suggested to simplify and streamline the presentation accordingly.
Response 4: After applying the ETM to validate the results by PFC, this study assigned the maximum contact deformation between the rockfall and the column to the initial displacement in the dynamic equation of the column. The initial displacement is the basis and premise of calculating energy. The two parts are not repeated and are essential.
Point 5:The article states that " according to the Hertz contact theory, the contact model of the shock process between polyhedron rockfall and the hydraulic support column is constructed, and the maximum deformation and maximum impact force of the collision contact between the rockfall and the column are obtained. Finally, the Hamilton principle and the Galerkin discrete method are used to construct the dynamic model of the collision between the rockfall and the column, and the energy evolution law of the shock process between rockfall and the column is studied" However, the paper does not present the parameters used in the calculations nor the computed results. Additionally, it fails to highlight the application of this model in numerical simulations. Furthermore, there is no comparison made between the numerical simulation results and the calculation results obtained from theoretical analysis, which is essential to validate the reliability of the findings.
Response 5:The parameters required for this sub-calculation have been supplemented in the paper. The parameters of rockfall and working face are shown in Table 1 and Table 2. The parameters of hydraulic support and column are shown in Table 3 and 294-300 lines in the paper. The simulation results are discussed in detail in Figs.8-11.
Additionally, the application of this model in numerical simulations would “provide a certain theoretical basis for the prediction of rockfall disasters and the design of rockfall protection devices”, as highlighted in the end of the Abstract, as well as in Introduction supported with References 13~31.
The numerical simulation results of this paper are obtained based on the theoretical analysis of this paper. Thanks for the reviewer’s comment, and it would greatly improve our future study by introducing experimental into the validation of the numerical simulations results (which are obtained based on theoretical analysis).
Point 6: References section: It is striking that all papers referenced are from Chinese authors; the literature review produced as a whole is very China-focused/restricted.
Response 6: We have newly added 12 references and revised the introduction. See lines 32-49. The research progress of mining theory and technology of SDCS in foreign countries is relatively slow, and there are few documents available for reference, and there is few research results on rockfall.
Point 7:The paper investigates the "Energy dissipation of support column structure under rockfall impact load in steeply dipping coal seams." However, it does not provide information regarding the deformation of hydraulic columns in the field or the parameters of the rockfall. It is unclear whether the results obtained from numerical simulations can be directly applied to real-world scenarios. I suggest the authors to further supplement the paper with relevant field data to support their findings.
Response 7: Firstly, in the manuscript, the information regarding the deformation of hydraulic columns in the field is presented: “The field measurement statistics of rockfall disasters shows that, when rockfalls damage equipment, this phenomenon mostly occurs on the hydraulic support column, as shown in Figure 2. [15] [20]”.
Secondly, thanks for the reviewer’s suggestions, we will introduce the experimental method to verify the accuracy of the method in this paper. If possible, in the future research the working face site should also be measured to achieve the purpose of mutual feedback verification.
Lastly, in the revised draft, Figure 7 quoted from the newly added Reference 43 shows the hydraulic support column ZZ6500/22/48, in order to supplement the paper.
Reviewer 3 Report
Dear Authors
Scientific comments
It is an interesting work; however, you should pay attention to:
The use of acronyms without description, e.g. line 107… uses PFC discrete element…
conclusion item you refer …The discrete 375 element method PFC3D software … The question is: did you establish a mesh of discrete finite elements and program it according to the variables or, you used a commercial or adapted program? Should clarify this in the article. You should better develop the methodology and equations used and pay attention to the description of all index variables and coefficients used in the equations. You should consider improving the understanding of the model and its application.
Equation 1 needs text that starts it and before it appears.
Pay attention to the units that must be in the IS; e.g. line 240 …range 4Gpa-6Gpa), rockfall density (value range 2000kg / m3… must be GPa and the density quantity in kN/m3, as in the tables. In Table 2 elasticity modulus must be in kN/m2.
Figure 8. The presentation and explanation should come before this one.
The bibliography is correct.
Editorial comments
Figure 5, consider putting the entire figure and legend on the same page.
Author Response
Response to Reviewer 3Comments
Point 1: The use of acronyms without description, e.g. line 107… uses PFC discrete element…
Response 1:The acronym “PFC” in line 107 in the original draft, now has been modified as “Particle flow code (PFC)” in line 117 in the revised draft, and other similar issues have also been addressed in the revised draft.
Point 2:conclusion item you refer The discrete 375 element method PFC3D software … The question is: did you establish a mesh of discrete finite elements and program it according to the variables or, you used a commercial or adapted program? Should clarify this in the article. You should better develop the methodology and equations used and pay attention to the description of all index variables and coefficients used in the equations. You should consider improving the understanding of the model and its application.
Response 2:Firstly, PFC3D software, a commercial program, is applied to simulate the rockfall migration model.
Secondly, to better demonstrate the application of PFC3D, in the revised draft the fundamental principle that PFC3D follows is presented in detail in lines 122-145, and the calculations process of PFC3D is also added in the revised draft as Figure 3.
Thirdly, to better improve the understanding of the study, more detailed information has been added in the revised draft, such as the side length of the rockfall in Table 1, the length of the working face in Table 2, the falling height in line 280, and so on.
Lastly, the application of the current study in would provide a certain theoretical basis for the prediction of rockfall disasters and the design of rockfall protection device as highlighted in the end of the Abstract, as well as in Introduction supported with References 13~31.
Point 3:Equation 1 needs text that starts it and before it appears.
Response 3:An explanation now has been added before Equation 1, as shown in line 158 in the revised draft: “The contact stress p is distributed in a semi-elliptical cylinder, and its value is”.
Point 4:Pay attention to the units that must be in the IS; e.g. line 240 …range 4Gpa-6Gpa), rockfall density (value range 2000kg /m3… must be GPa and the density quantity in kN/m3, as in the tables. In Table 2 elasticity modulus must be in kN/m2.
Response 4: All units in the revised draft have been checked and now they are all in accordance with IS.
Point 5: Figure 8. The presentation and explanation should come before this one.
Response 5:All presentation and explanation regarding Figure 11(Figure 8) now have been placed before the figure, as shown in the revised draft in lines 402-435.
Point 6：Figure 5, consider putting the entire figure and legend on the same page.
Response 6:Thanks for the comments, and now the entire figure and legend have be put on the same page in the revised draft.
Round 2
Reviewer 1 Report
（1）The authors should provide mechanical model of this physical process, and the sketch of the numerical model as well as typical contour maps during the simulation output by the software.
(2) The quality of the figures need to be improved, since not much useful information can be obtained in the figures (Fig. 1, Fig. 5, Fig.7-Fig.9 ).
Author Response
Response to Reviewer 1Comments
Point 1:The authors should provide mechanical model of this physical process, and the sketch of the numerical model as well as typical contour maps during the simulation output by the software.
Response 1: The mechanical contact model of particle flow theory is supplemented, as shown in Fig.4,158 lines-166 lines.
The mechanical model of rockfall impact the midpoint of hydraulic support column is shown in Fig. 7.
The horizontal projection of the contour line of the coal seam floor is shown in Fig. 8.
The wave diagram of the midpoint of the column is shown in Fig.10.
Point 2:The quality of the figures need to be improved, since not much useful information can be obtained in the figures (Fig. 1, Fig. 5, Fig.7-Fig.9 ).
Response 2: Fig. 1, Fig. 5 and Fig.7 have been deleted.
The schematic diagram of the rockfall migration trajectory in Fig. 1 is supplemented.
Coal wall spalling is the main source of rockfall, a nine-month information collection of coal wall spalling was carried out in a steeply inclined working face from October 2012 to July 2013, the statistical results are shown in Fig. 3 and Table 1. And lines 110-146 illustrate the mechanism of rockfall separation.
In order to display the results more clearly and intuitively, Figure 11-Figure 28 supplements the corresponding two-dimensional diagram.
Reviewer 2 Report
The study is interesting, but the current version of this manuscript can not meet the standard of publication. The results are too simplistic. It is suggested to enrich and strengthen the numerical simulation part of the paper, supplement the field data, simplify the theoretical analysis part, and add more relevant images to highlight the research significance proposed in the paper.
Author Response
Response to Reviewer 2Comments
Point 1:The results are too simplistic. It is suggested to enrich and strengthen the numerical simulation part of the paper.
Response 1:The wave diagram of the midpoint of the column supplemented, as shown in Fig.10.
In order to display the results more clearly and intuitively, Figure 11-Figure 28 supplements the corresponding two-dimensional diagram.
The energy impact ranking table is supplemented, see table 4.
Point 2:supplement the field data.
Response 2:A nine-month information collection of coal wall spalling was carried out in a steeply inclined working face from October 2012 to July 2013, the statistical results are shown in Fig. 3 and Table 1. Lines 110-146 illustrate the mechanism of rockfall separation.
Point 3:Simplify the theoretical analysis part.
Response 3:The theoretical analysis part was reorganized, the formula 3-7 was deleted, and the formula 14-15 was merged.
Point 4:Add more relevant images to highlight the research significance proposed in the paper.
Response 4:The schematic diagram of the rockfall migration trajectory in Fig. 1 is supplemented.
The mechanical contact model of particle flow theory is supplemented, as shown in Fig.4.
The mechanical model of rockfall impact the midpoint of hydraulic support column is shown in Fig. 7.
The horizontal projection of the contour line of the coal seam floor is shown in Fig. 8.
The wave diagram of the midpoint of the column is shown in Fig.10.
Coal wall spalling is the main source of rockfall, a nine-month information collection of coal wall spalling was carried out in a steeply inclined working face from October 2012 to July 2013, the statistical results are shown in Fig. 3.
Round 3
Reviewer 1 Report
（1）The author's understanding of review comment 1 is incorrect. What I mean is that the sketch of the numerical model as well as some typical contour maps output by the software are recommended to be added in the manuscript.
（2）There are still some spelling mistakes in the manuscript, for instance, line 54, line 125, 314, 336, etc.
(3) References 1-12 have little to do with the content of the article.
English is very difficult to understand/incomprehensible.
Author Response
Please see the attachment。
Author Response File: 
Author Response.pdf
Reviewer 2 Report
I suggest reducing the number of theoretical formulas in sections two to four of the paper. Additionally, in section five, there is a high level of image repetition, which could be optimized. The conclusion lacks critical and in-depth content, so further refinement of the language is need.
Author Response
Response to Reviewer 2Comments
Point 1: I suggest reducing the number of theoretical formulas in sections two to four of the paper.
Response 1: All formulas have been sorted out and eight theoretical formulas have been deleted.
Point 2: In section five, there is a high level of image repetition, which could be optimized.
Response 2: The image has been optimized and adjusted, nine images have been deleted, and the analysis part has been refined, see lines 331-397.
Point 3: The conclusion lacks critical and in-depth content, so further refinement of the language is need.
Response 3: The conclusion part of the language has been further refined, see 442-448 lines.
